" The original Lumicon Ultra-High-Contrast narrow bandpass filter (24nm) isolates just the two doubly-ionized oxygen lines (496 and 501nm lines) and H-beta line (486nm) emitted by planetary and most emission nebulae, while blocking, completely the rest of the overall spectrum of light. The result is extreme contrast between the black background of space and the delicate photons of nebula light needed for near-photographic views of the Orion, Lagoon, Swan and planetary nebulae, among others. This makes the Lumicon UHC Filter the best all-around dark-sky nebular filter on the market today. See for yourself -- it's truly amazing what the Lumicon UHC filter allows you to see! Lumicon tests every filter individually on a Perkin-Elmer Double Beam spectrophotometer, inscribing on the filter its % transmission for each of the primary lines. Do not settle for cheap, foreign-made imitations. "